The present invention relates to a method of detecting a solid shape of an object. The present invention relates to the method of detecting a solid shape of an object, by aiming at focus levels of an optical image of an object.
An example of the method of detecting a solid shape of an object, by aiming at focus levels, has been disclosed in the Japanese Patent Application Laid-Open No. 61-124809. According to this method, with respect to a rugged pattern which constitutes an object to be inspected, respective pattern detection is made by changing focus levels, thereby permitting calculation of plane and solid dimensions of the pattern from such information of focus levels and information of pattern positions. To be more concrete, in taking an LSI wafer pattern as an example, pattern images whose focal planes are successively changed by a focus adjustment mechanism are detected, and by extracting and synthesizing the sharpest portions of such image signals, the following will become possible:
(i) Detection of step edges of a pattern, in focus with either an upper edge of a step or a lower edge of a step in step edges of the pattern.
(ii) Detection of solid dimensions (thickness) of a pattern from focus levels in case the sharpest portion is extracted.
(iii) In the case of a photoresist pattern, from the image signal having maximum contrast, detection of the upper and lower edge levels in step edges of the pattern as the maximum rate of such changes.
On the other hand, according to a paper by Takatoshi Ota et al., entitled "A Method for Image Composition Using Image Variance", Journal of the Institute of Electronics and Communication Engineers of Japan, '83/10 Vol. J66-D No. 10, pp.1245-1246, it is possible to obtain an image, well-focused on the entire image, by looking for the brightness variance in each local region from object images with different focus levels and by extracting and synthesizing a focused region in each image therefrom.